The cholesterol content in the plasma membranes of cultured normal or transformed cells can be reduced by blockage of sterol biosynthesis with several oxygenated derivatives of cholesterol. The effect of the alteration of membrane sterol content on several biological activities which are associated with surface membrane of cells will be studied. These activities include osmotic fragility of the membrane, permeability of cells to solutes (e.g., glycerol, acetate and erythritol), and fluidity of the surface membrane. The relationship between the synthesis of cholesterol and cell proliferation in synchronized normal and transformed cell cultures and in lymphocytes and leukemic cells will be examined. BIBLIOGRAPHIC REFERENCES: Kandutsch, A.A., H.-J. Heiniger, and H.W. Chen. 1977. Effects of 25-hydroxycholesterol and 7-ketocholesterol - inhibitors of sterol synthesis - administered orally to mice. Biochim. Biophys. Acta (in press). Kandutsch, A.A., and H.W. Chen. 1977. Consequences of blocked sterol synthesis in cultured cells: DNA synthesis and membrane composition. J. Biol. Chem. (in press).